This project studies the pathophysiological and hormonal regulation of membrane transport systems and the mechanisms by which age-dependent changes pertub physiological control systems and, thus, contribute to the failure to maintain hemeostasis in the aged. This project represents a continuation and extension of previous projects - Z01 AG 00041-07 LMA and Z01 AG 00042-07 LMA. Notable scientific achievements include: (1) The discovery was made that glucocorticoids increase sodium-proton exchange activity which represents the major mechanism for acid secretion and bicarbonate reabsorption in the proximal tubule; (2) In chronic uremia, sodium gradient-dependent phosphate uptake was decreased. Thyroparathyroidectomy restored the activity; (3) Parathyroid hormone-mediated decrease in phosphate uptake was found to be concomitant with the phosphorylation of specific membrane proteins; (4) Membrane enzymes from aged animals was discovered to have altered conformation with increased antigenic sites; (5) Hybridoma technology for the production of monoclonal antibodies against specific membrane carriers was developed to determine how the proteins change during aging and in different pathophysiological states; (6) A new technique for the preparation of renal cortical baso-lateral membrane vesicles was developed.